Polarizing plate

ABSTRACT

A polarizing plate according to an embodiment of the present invention includes a polarizing film having a thickness of 10 μm or less and a protective layer provided on at least one side of the polarizing film through intermediation of an adhesion layer. The adhesion layer has a thickness of 0.7 μm or more, and the adhesion layer has a percentage of bulk water absorption of 10 wt % or less.

This application claims priority under 35 U.S.C. Section 119 to JapanesePatent Application No. 2014-158697 filed on Aug. 4, 2014, which areherein incorporated by references.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polarizing plate.

2. Description of the Related Art

A polarizing plate is used in an image display apparatus (such as aliquid crystal display apparatus). The polarizing plate generallyincludes a polarizing film and a protective layer for protecting thepolarizing film. In recent years, it has been demanded that the imagedisplay apparatus be thinned, and in this connection, it has beendemanded the polarizing plate be thinned.

Incidentally, there is a proposal of a method involving forming apolyvinyl alcohol-based resin layer on a resin substrate, and stretchingand dyeing the resultant laminate to provide a polarizing film (forexample, Japanese Patent Application Laid-open No. 2000-338329).According to such method, a polarizing film having a small thickness(for example, 10 μm or less) is obtained, and hence the method has beenattracting attention for its capability to contribute to the thinning ofthe image display apparatus. However, when the thickness of thepolarizing film is reduced, the polarizing plate to be obtained has aproblem in that its external appearance is poor.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve the conventionalproblems, and a primary object of the present invention is to provide apolarizing plate excellent in external appearance.

According to one aspect of the present invention, a polarizing plate isprovided. The polarizing plate includes a polarizing film having athickness of 10 μm or less and a protective layer provided on at leastone side of the polarizing film through intermediation of an adhesionlayer. The adhesion layer has a thickness of 0.7 μm or more, and theadhesion layer has a percentage of bulk water absorption of 10 wt % orless.

In one embodiment of the present invention, the polarizing film has avalue for Aa×(Is/Ia) of 0.53 or more. The Aa represents an absorbance ofthe polarizing film in an absorption axis direction thereof at awavelength of 480 nm. The Ia represents a value obtained by integratingan integrated intensity distribution of an integrated intensity in athickness direction of the polarizing film in an entire interval in thethickness direction of the polarizing film, the integrated intensitybeing obtained by integrating a Raman spectrum of the polarizing film ina wavenumber interval from 90 cm⁻¹ to 120 cm⁻¹. The Is represents avalue obtained by integrating an integrated intensity distribution of anintegrated intensity in the thickness direction of the polarizing filmin the entire interval in the thickness direction of the polarizingfilm, the integrated intensity being obtained by integrating Ramanscattering of I₃ ⁻ that is present in a portion ranging from apolarizing film surface to a depth of 1 μm in the thickness direction ofthe polarizing film, and that is aligned in the absorption axisdirection of the polarizing film in the wavenumber interval from 90 cm⁻¹to 120 cm⁻¹.

In another embodiment of the present invention, the thickness of theadhesion layer is 2 μm or less.

In still another embodiment of the present invention, the percentage ofbulk water absorption of the adhesion layer is 0.05 wt % or more.

In still another embodiment of the present invention, the adhesion layeris formed by curing a curable adhesive.

In still another embodiment of the present invention, the adhesion layerhas a storage modulus in a region of 70° C. or less of from 1.0×10⁶ Pato 1.0×10¹⁰ Pa.

According to another aspect of the present invention, an image displayapparatus is provided. The image display apparatus includes thepolarizing plate.

According to one embodiment of the present invention, the protectivelayer is provided on the polarizing film through the intermediation ofthe adhesion layer having a thickness of 0.7 μm or more, and thus thegeneration of air bubbles can be effectively suppressed. As a result, apolarizing plate excellent in external appearance can be obtained. Inaddition, the percentage of bulk water absorption of the adhesion layeris set to 10 wt % or less, and thus a polarizing plate that also hasdurability can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a polarizing plateaccording to one embodiment of the present invention.

FIG. 2 is a graph showing a relationship between absorbance andwavelength in the case where polarized light parallel to the absorptionaxis of a polarizing film is allowed to enter.

FIG. 3 is one example of a Raman spectrum of a polarizing film.

FIG. 4 is an example of the distribution of integrated intensities in awavenumber interval from 90 cm⁻¹ to 120 cm⁻¹ in Raman spectra atrespective measurement points of a polarizing film based on Ramanspectroscopy.

FIG. 5 is a graph showing a relationship between the integratedintensity distribution of I₃ ⁻ after smoothing processing and theposition of a laser light spot in the approximation of Is.

FIG. 6 is a diagram illustrating a method of producing a sample forRaman spectrometry.

FIG. 7 is a diagram illustrating a Raman spectrometric method.

FIG. 8A is a photograph showing the evaluation result of durability ofComparative Example 2, and FIG. 8B is a photograph showing theevaluation result of durability of Example 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are described below. However, thepresent invention is not limited to these embodiments.

FIG. 1 is a schematic cross-sectional view of a polarizing plateaccording to one embodiment of the present invention. A polarizing plate100 includes a polarizing film 10, a first protective layer 21 providedon one side of the polarizing film 10, and a second protective layer 22provided on the other side of the polarizing film 10. The firstprotective layer 21 is provided on the polarizing film 10 through theintermediation of a first adhesion layer 31. The second protective layer22 is provided on the polarizing film 10 through the intermediation of asecond adhesion layer 32. When the protective layers are respectivelyprovided on both sides of the polarizing film as in the illustratedexample, the protective layers may have the same construction, or mayhave different constructions.

A. Polarizing Film

The polarizing film is typically a polyvinyl alcohol-based resin(hereinafter referred to as “PVA-based resin”) membrane having adichromatic substance adsorbed and aligned thereon. The polarizing filmhas a thickness of preferably 10 μm or less, more preferably 7 μm orless, particularly preferably 5 μm or less. On the other hand, thethickness of the polarizing film is preferably 0.5 μm or more, morepreferably 1.0 μm or more.

The polarizing film preferably exhibits absorption dichroism at anywavelength in the wavelength range of from 380 nm to 780 nm. Thepolarizing film has a single axis transmittance of preferably 40.0% ormore, more preferably 41.0% or more, still more preferably 42.0% ormore, particularly preferably 43.0% or more. The polarizing film has apolarization degree of preferably 99.8% or more, more preferably 99.9%or more, still more preferably 99.95% or more.

Examples of the dichromatic substance include iodine and an organic dye.The substances may be used alone or in combination. Iodine is preferredas the dichromatic substance.

Any appropriate resin may be adopted as a PVA-based resin for formingthe PVA-based resin membrane. Examples of the resin include polyvinylalcohol and an ethylene-vinyl alcohol copolymer. The polyvinyl alcoholis obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcoholcopolymer is obtained by saponifying an ethylene-vinyl acetatecopolymer. The saponification degree of the PVA-based resin is typicallyfrom 85 mol % to 100 mol %, preferably from 95.0 mol % to 99.95 mol %,more preferably from 99.0 mol % to 99.93 mol %. The saponificationdegree may be determined in conformity with JIS K 6726-1994. The use ofthe PVA-based resin having such saponification degree can provide apolarizing film excellent in durability. When the saponification degreeis excessively high, gelling may occur.

The average polymerization degree of the PVA-based resin may beappropriately selected depending on purposes. The average polymerizationdegree is typically from 1,000 to 10,000, preferably from 1,200 to4,500, more preferably from 1,500 to 4,300. It should be noted that theaverage polymerization degree may be determined in conformity with JIS K6726-1994.

In one embodiment, the polarizing film has a value for Aa×(Is/Ia) of0.53 or more, where: Aa represents the absorbance of the polarizing filmin the absorption axis direction thereof at a wavelength of 480 nm; Iarepresents a value obtained by integrating the integrated intensitydistribution of an integrated intensity in the thickness direction ofthe polarizing film in the entire interval in the thickness direction ofthe polarizing film, the integrated intensity being obtained byintegrating a Raman spectrum of the polarizing film in a wavenumberinterval from 90 cm⁻¹ to 120 cm⁻¹; and Is represents a value obtained byintegrating the integrated intensity distribution of an integratedintensity in the thickness direction of the polarizing film in theentire interval in the thickness direction of the polarizing film, theintegrated intensity being obtained by integrating Raman scattering ofI₃ ⁻ that is present in a portion ranging from a polarizing film surfaceto a depth of 1 μm in the thickness direction of the polarizing film,and that is aligned in the absorption axis direction of the polarizingfilm in the wavenumber interval from 90 cm⁻¹ to 120 cm⁻¹. Further, thevalue for Aa×(Is/Ia) may be set to 0.55 or more.

As described later in detail, the Aa×(Is/Ia) is an indicator for theiodine concentration of the polarizing film surface. A polarizing filmhaving a small thickness (a thickness of 10 μm or less) has a highiodine concentration, and may show the above-mentioned value forAa×(Is/Ia). It should be noted that the iodine amount of the polarizingfilm to be obtained may not be uniform in its thickness directiondepending on its production method. For example, a polarizing film inwhich iodine is uniformly present in its thickness direction can beobtained by adopting an underwater stretching mode to be describedlater.

The meaning of the absorbance Aa of the polarizing film in theabsorption axis direction thereof at the wavelength of 480 nm isdescribed. FIG. 2 shows a graph showing a relationship betweenabsorbance and wavelength in the case where polarized light parallel tothe absorption axis of the polarizing film is allowed to enter. In thepolarizing film that is a PVA-based resin membrane having iodineadsorbed thereon, the adsorbed iodine is said to take the form of acomplex of a polyiodide ion such as I₃ ⁻ or I₅ ⁻ with PVA. In FIG. 2, itis known that absorption around 480 nm corresponds to I₃ ⁻ in the formof a complex with PVA, and absorption around 600 nm corresponds to I₅ ⁻in the form of a complex with PVA.

According to the Lambert-Beer law, the absorbance A of a certain mediummay be generally represented by A=εcL where ε represents the molarabsorption coefficient of the medium, represents the molar concentrationof the medium, and L represents a cell (optical path) length. This givescL=A/ε, and hence the absorbance serves as an indicator for the amountof the medium per unit area in the entire film thickness of thepolarizing film (area density of the medium). Therefore, although themolar absorption coefficient of each of I₃ ⁻ and I₅ ⁻ in the form of acomplex with PVA is difficult to determine, the amount of I₃ ⁻ in theform of a complex with PVA that is aligned in the absorption axisdirection of the polarizing film per unit area in the entire filmthickness of the polarizing film may be represented by using theabsorbance Aa of the polarizing film in the absorption axis directionthereof at 480 nm as an indicator.

The absorbance Aa of the polarizing film in the absorption axisdirection thereof at 480 nm is an indicator for the amount of I₃ ⁻ inthe form of a complex with PVA that is aligned in the absorption axisdirection of the polarizing film per unit area in the entire filmthickness of the polarizing film. Accordingly, an indicator for theamount of I₃ ⁻ in the form of a complex with PVA that is aligned in theabsorption axis direction of the polarizing film in a portion in thevicinity of the polarizing film surface can be determined when its ratiowith respect to the entire thickness direction is found. Herein, it isassumed that the amount of I₃ ⁻ in the form of a complex with PVA thatis aligned in the absorption axis direction of the polarizing film inthe portion in the vicinity of the polarizing film surface is the amountof I₃ ⁻ in the form of a complex with PVA that is present in a portionranging from the polarizing film surface to a depth of 1 μm in thethickness direction of the polarizing film, and that is aligned in theabsorption axis direction of the polarizing film.

Raman spectroscopy is known as means for evaluating the amount of I₃ ⁻or I₅ ⁻ in a polarizing film. The Raman spectroscopy is a methodinvolving allowing laser light having a single wavelength in anultraviolet to near-infrared region to enter, and detecting Ramanscattered light that results from the vibration of a molecular skeleton.FIG. 3 shows an example of a Raman spectrum of a polarizing filmobtained by Raman spectroscopy using laser light having a polarizationplane parallel to the absorption axis direction of the polarizing filmand having a wavelength of 514.5 nm. In this Raman spectrum, it is knownthat a peak around 108 cm⁻¹ is attributable to I₃ ⁻ that is aligned inthe absorption axis direction of the polarizing film, and a peak around158 cm⁻¹ is attributable to I₅ ⁻ that is aligned in the absorption axisdirection of the polarizing film. Thus, the integrated intensityobtained by integration in a predetermined wavenumber interval in thevicinity of the peak around a wavenumber of 108 cm⁻¹ in the Ramanspectrum may be used as an indicator for the amount of I₃ ⁻ that isaligned in the absorption axis direction of the polarizing film at ameasurement point.

A wavenumber interval from 90 cm⁻¹ to 120 cm⁻¹ is adopted as thepredetermined wavenumber interval. In addition, baseline correction isperformed for Raman intensity. Referring now to FIG. 3, the baselinecorrection refers to the following operation: in the wavenumber intervalfrom 90 cm⁻¹ to 120 cm⁻¹, a straight line connecting the respectivepoints a and b of a Raman intensity at a wavenumber of 90 cm⁻¹ and aRaman intensity at a wavenumber of 120 cm⁻¹ is used to approximate thebaseline of the Raman spectrum as a straight line, and a distance fromthe approximation straight line is defined as a Raman intensity tocorrect the slope of the baseline at the time of measurement.

In order to determine the ratio of the amount of I₃ ⁻ that is present inthe portion ranging from the polarizing film surface to a depth of 1 μmin the thickness direction of the polarizing film, and that is alignedin the absorption axis direction of the polarizing film to the amount inthe entire thickness direction of the polarizing film, first, a Ramanspectrum is measured for a cross-section of the polarizing film whilemoving a measurement point in the thickness direction, to therebydetermine the distribution of integrated intensities in the wavenumberinterval from 90 cm⁻¹ to 120 cm⁻¹ at respective measurement points. FIG.4 shows an example of the resultant integrated intensity distribution(polarizing film of Example 2 to be described later). It should be notedthat the origin of the thickness direction in the figure corresponds tothe position of an inflection point to be described later, and it isassumed that light is allowed to enter from a negative coordinate side.In FIG. 4, i.e., the graph of the integrated intensity distribution inthe thickness direction of the polarizing film, the value Ia obtained byintegrating the integrated intensity distribution in the entire intervalin the thickness direction of the polarizing film corresponds to theRaman scattering of I₃ ⁻ that is present in the entire thicknessdirection of the polarizing film, and that is aligned in the absorptionaxis direction of the polarizing film, and hence is considered toindicate the amount of I₃ ⁻ that is aligned in the absorption axisdirection of the polarizing film in the entire thickness direction ofthe polarizing film.

Ia is determined as the integral of the integrated intensity that hasbeen subjected to smoothing processing with a weighted moving average.In the smoothing processing, an integrated intensity at a position x inthe thickness direction before the smoothing processing is representedby I(x), and an integrated intensity I_(WMA)(x) after the smoothingprocessing is determined by the following equation.

I_(WMA)(x)=[I(x−0.5)×1+I(x−0.4)×2+I(x−0.3)×4+I(x−0.2)×6+I(x−0.1)×8+I(x)×10+I(x+0.1)×8+I(x+0.2)×6+I(x+0.3)×4+I(x+0.4)×2+I(x+0.5)×1]/(1+2+4+6+8+10+8+6+4+2+1)

FIG. 4 shows an example of the resultant integrated intensitydistribution after the smoothing processing.

In addition, the amount of I₃ ⁻ that is present in the portion rangingfrom the polarizing film surface to a depth of 1 μm in the thicknessdirection of the polarizing film, and that is aligned in the absorptionaxis direction of the polarizing film corresponds to the Ramanscattering of I₃ ⁻ that is present in the portion ranging from thepolarizing film surface to a depth of 1 μm in the thickness direction ofthe polarizing film, and that is aligned in the absorption axisdirection of the polarizing film. Therefore, the value Is obtained byintegrating the integrated intensity distribution of an integratedintensity in the thickness direction of the polarizing film in thethickness direction of the polarizing film, the integrated intensitybeing obtained by integrating the Raman scattering of I₃ ⁻ that ispresent in the portion ranging from the polarizing film surface to adepth of 1 μm in the thickness direction of the polarizing film, andthat is aligned in the absorption axis direction of the polarizing filmin the wavenumber interval from 90 cm⁻¹ to 120 cm⁻¹, is considered toindicate the amount of I₃ ⁻ that is present in the portion ranging fromthe polarizing film surface to a depth of 1 μm in the thicknessdirection of the polarizing film, and that is aligned in the absorptionaxis direction of the polarizing film.

Therefore, because it is considered that the ratio of the amount of I₃ ⁻in the form of a complex with PVA that is present in the portion rangingfrom the polarizing film surface to a depth of 1 μm in the thicknessdirection of the polarizing film, and that is aligned in the absorptionaxis direction of the polarizing film to the amount of I₃ ⁻ in the formof a complex with PVA that is aligned in the absorption axis directionof the polarizing film in the entire thickness direction of thepolarizing film may be approximated by the ratio of the amount of I₃ ⁻that is present in the portion ranging from the polarizing film surfaceto a depth of 1 μm in the thickness direction of the polarizing film,and that is aligned in the absorption axis direction of the polarizingfilm to the amount of I₃ ⁻ that is aligned in the absorption axisdirection of the polarizing film in the entire thickness direction ofthe polarizing film, the Aa×(Is/Ia) serves as an indicator for theamount of I₃ ⁻ in the form of a complex with PVA that is present in theportion ranging from the polarizing film surface to a depth of 1 μm inthe thickness direction of the polarizing film, and that is aligned inthe absorption axis direction of the polarizing film.

In this context, the amount of I₃ ⁻ that is present in the portionranging from the polarizing film surface to a depth of 1 μm in thethickness direction of the polarizing film, and that is aligned in theabsorption axis direction of the polarizing film corresponds to thevalue Is obtained by integrating the distribution curve (partialdistribution curve) of the integrated intensity in the entire intervalin the thickness direction of the polarizing film, the integratedintensity corresponding to the Raman scattering of I₃ ⁻ that is presentin the portion ranging from the polarizing film surface to a depth of 1μm in the thickness direction of the polarizing film, and that isaligned in the absorption axis direction of the polarizing film, but thevalue Is cannot be accurately determined. Accordingly, the value Isobtained by integrating the integrated intensity distribution of theintegrated intensity in the thickness direction of the polarizing filmin the entire interval in the thickness direction of the polarizingfilm, the integrated intensity being obtained by integrating the Ramanscattering of I₃ ⁻ that is present in the portion ranging from thepolarizing film surface to a depth of 1 μm in the thickness direction ofthe polarizing film, and that is aligned in the absorption axisdirection of the polarizing film in the wavenumber interval from 90 cm⁻¹to 120 cm⁻¹, is approximately determined.

Referring to FIG. 5, first, in the integrated intensity distributionafter the smoothing processing obtained as described above in thecalculation of Ia, an inflection point at a rise on the side on whichlight enters is determined. Assuming that the spot cross-section oflaser light to be used in the Raman analysis is circular, when thecenter of the spot cross-section is located at a position on thepolarizing film surface, it is considered that the rate of change inarea of the cross-section of the polarizing film irradiated with thelaser light becomes a local maximum and the rate of change in integratedintensity of the Raman scattering of I₃ ⁻ becomes a local maximum.Accordingly, the position of the inflection point may be presumed to besubstantially a position on the polarizing film surface.

Next, when the spot cross-section of the laser light is located at thecenter of the portion ranging from the polarizing film surface to adepth of 1 μm in the thickness direction of the polarizing film, i.e., aposition of 0.5 μm from the polarizing film surface, the ratio of Ramanscattering from I₃ ⁻ that is present in a portion other than the portionranging from the polarizing film surface to a depth of 1 μm in thethickness direction of the polarizing film or from air to a measuredvalue is smallest as compared to that in the case where the spotcross-section of the laser light is located at any other position. Thus,the integrated intensity in the case where the spot cross-section of thelaser light is located at a position of +0.5 μm from the polarizing filmsurface is considered to best indicate the value for the integratedintensity corresponding to the Raman scattering of I₃ ⁻ that is presentin the portion ranging from the polarizing film surface to a depth of 1μm in the thickness direction of the polarizing film. Accordingly, Is isdetermined by the following approximation: the integrated intensitydistribution of the integrated intensity in the thickness direction ofthe polarizing film, the integrated intensity being obtained byintegrating the Raman scattering of I₃ ⁻ that is present in the portionranging from the polarizing film surface to a depth of 1 μm in thethickness direction of the polarizing film, and that is aligned in theabsorption axis direction of the polarizing film in the wavenumberinterval from 90 cm⁻¹ to 120 cm⁻¹, is regarded as constant at a valueI_(WMA)(0.5) for the integrated intensity after the smoothing processingat the position of +0.5 μm from the inflection point in the intervalfrom the polarizing film surface to 1 μm, and is regarded as zero in anyother interval. That is, approximation is performed by Is=I_(WMA)(0.5)×1=I_(WMA)(0.5).

Any appropriate method may be adopted as a manufacturing method for thepolarizing film. The polarizing film is typically manufactured bysubjecting a PVA-based resin membrane to various treatments. Anyappropriate form may be adopted for the PVA-based resin membrane to besubjected to various treatments. Specifically, a PVA-based resin filmmay be adopted, or a PVA-based resin layer formed on a resin substratemay be adopted.

In one embodiment, the polarizing film is manufactured by forming aPVA-based resin layer on a resin substrate to produce a laminate, andsubjecting the laminate to various treatments. The PVA-based resin layeris formed by, for example, applying an application liquid containing aPVA-based resin onto the resin substrate. A solution prepared bydissolving the PVA-based resin in a solvent is typically used as theapplication liquid. Examples of the solvent to be used for dissolvingthe PVA-based resin include water, dimethylsulfoxide, dimethylformamide,dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydricalcohols such as trimethylolpropane, and amines such as ethylenediamineand diethylenetriamine. The solvents may be used alone or incombination. Of those, water is preferred. The concentration of thePVA-based resin in the solution is preferably from 3 parts by weight to20 parts by weight with respect to 100 parts by weight of the solvent.

The application liquid may contain an additive. Examples of the additiveinclude a plasticizer and a surfactant. Examples of the plasticizerinclude polyhydric alcohols such as ethylene glycol and glycerin. Anexample of the surfactant is a nonionic surfactant. Such additive may beused for the purpose of additionally improving the uniformity, dyeingproperty, or stretchability of the PVA-based resin layer to be obtained.Another example of the additive is an easy-adhesion component. The useof the easy-adhesion component can improve adhesiveness between theresin substrate and the PVA-based resin layer. As a result, for example,a problem such as the peeling of the PVA-based resin layer from theresin substrate is suppressed, and thus dyeing and underwater stretchingto be described later can be satisfactorily performed. For example,modified PVA such as acetoacetyl-modified PVA is used as theeasy-adhesion component.

Any appropriate method may be adopted as a method of applying theapplication liquid. Examples of the method include a roll coatingmethod, a spin coating method, a wire bar coating method, a dip coatingmethod, a die coating method, a curtain coating method, a spray coatingmethod, and a knife coating method (comma coating method or the like).

The application temperature of the application liquid is preferably 50°C. or more. A coat of the application liquid is preferably dried. Thedrying temperature is preferably 50° C. or more.

The thickness of the PVA-based resin layer (before stretching) ispreferably from 3 μm to 40 μm, more preferably from 3 μm to 20 μm.

Any appropriate material may be adopted as a constituent material forthe resin substrate. Examples of the material include an ester-basedresin such as a polyethylene terephthalate-based resin, acycloolefin-based resin, an olefin-based resin such as polypropylene, a(meth)acrylic resin, a polyamide-based resin, a polycarbonate-basedresin, and a copolymer resin thereof. Of those, a polyethyleneterephthalate-based resin is preferably used. In particular, anamorphous polyethylene terephthalate-based resin is preferably used.Specific examples of the amorphous polyethylene terephthalate-basedresin include: a copolymer further containing isophthalic acid as adicarboxylic acid; and a copolymer further containingcyclohexanedimethanol as a glycol.

The glass transition temperature (Tg) of the resin substrate ispreferably 100° C. or less. When such resin substrate is used, in thestretching of a laminate to be described later, stretchability(particularly in underwater stretching) can be sufficiently securedwhile the crystallization of the PVA-based resin is suppressed. As aresult, a polarizing film having excellent optical properties (forexample, a polarization degree) can be manufactured. On the other hand,the glass transition temperature of the resin substrate is preferably60° C. or more. It should be noted that the glass transition temperature(Tg) is a value determined in conformity with JIS K 7121.

The thickness of the resin substrate is preferably from 20 μm to 300 μm,more preferably from 50 μm to 200 μm. A surface of the resin substratemay be subjected to surface modification treatment (e.g., coronatreatment), or may have an easy-adhesion layer formed thereon.

Examples of the various treatments include dyeing treatment, stretchingtreatment, insolubilizing treatment, cross-linking treatment, washingtreatment, and drying treatment. The treatments may be appropriatelyselected depending on purposes. In addition, the order, timing, numberof times, and the like of the treatments may be appropriately set. Therespective treatments are described below.

(Dyeing Treatment)

The dyeing treatment is typically performed by dyeing the PVA-basedresin membrane with a dichromatic substance. The dyeing treatment ispreferably performed by causing the PVA-based resin membrane to adsorb adichromatic substance. A method for the adsorption is, for example, amethod involving immersing the PVA-based resin membrane (laminate) in adyeing liquid containing a dichromatic substance, a method involvingapplying the dyeing liquid onto the PVA-based resin membrane, or amethod involving spraying the dyeing liquid on the PVA-based resinmembrane. Of those, a method involving immersing the laminate in thedyeing liquid is preferred. This is because the dichromatic substancecan satisfactorily adsorb to the membrane.

When iodine is used as the dichromatic substance, the dyeing liquid ispreferably an aqueous solution of iodine. The compounding amount ofiodine is preferably from 0.1 part by weight to 0.5 part by weight withrespect to 100 parts by weight of water. The aqueous solution of iodineis preferably compounded with an iodide in order that the solubility ofiodine in water may be increased. Examples of the iodide includepotassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminumiodide, lead iodide, copper iodide, barium iodide, calcium iodide, tiniodide, and titanium iodide. Of those, potassium iodide is preferred.The compounding amount of the iodide is preferably from 0.02 part byweight to 20 parts by weight, more preferably from 0.1 part by weight to10 parts by weight with respect to 100 parts by weight of water.

The liquid temperature of the dyeing liquid at the time of the dyeing ispreferably from 20° C. to 50° C. in order that the dissolution of thePVA-based resin may be suppressed. When the PVA-based resin membrane isimmersed in the dyeing liquid, an immersion time is preferably from 5seconds to 5 minutes in order that the transmittance of the PVA-basedresin membrane may be secured. In addition, the dyeing conditions (theconcentration, the liquid temperature, and the immersion time) may beset so that the polarization degree or single axis transmittance of thepolarizing film to be finally obtained may fall within a predeterminedrange. In one embodiment, the immersion time is set so that thepolarization degree of the polarizing film to be obtained may be 99.98%or more. In another embodiment, the immersion time is set so that thesingle axis transmittance of the polarizing film to be obtained may befrom 40% to 44%.

(Stretching Treatment)

Any appropriate method may be adopted as a method of stretching thelaminate. Specifically, fixed-end stretching (e.g., a method involvingusing a tenter stretching machine) may be adopted, or free-endstretching (e.g., a method involving passing the laminate between rollshaving different peripheral speeds to uniaxially stretch the laminate)may be adopted. Alternatively, simultaneous biaxial stretching (e.g., amethod involving using a simultaneous biaxial stretching machine) may beadopted, or sequential biaxial stretching may be adopted. The stretchingof the laminate may be performed in one stage, or may be performed in aplurality of stages. When the stretching is performed in a plurality ofstages, the stretching ratio (maximum stretching ratio) of the laminateto be described later is the product of stretching ratios in therespective stages.

The stretching treatment may be an underwater stretching mode, in whichstretching is performed while the laminate is immersed in a stretchingbath, or may be an in-air stretching mode. It is preferred thatunderwater stretching treatment be performed at least once, and it ismore preferred that underwater stretching treatment and in-airstretching treatment be performed in combination. According to theunderwater stretching, the stretching can be performed at a temperaturelower than the glass transition temperature (typically about 80° C.) ofeach of the resin substrate and the PVA-based resin membrane, and hencethe PVA-based resin membrane can be stretched at a high ratio while itscrystallization is suppressed. As a result, a polarizing film havingexcellent optical characteristics (e.g., polarization degree) can bemanufactured.

Any appropriate direction may be selected as a direction in which thelaminate is stretched. In one embodiment, the laminate having anelongate shape is stretched in its longitudinal direction. Specifically,the laminate is conveyed in its longitudinal direction, and is stretchedin its conveying direction (MD). In another embodiment, the laminatehaving an elongate shape is stretched in its width direction.Specifically, the laminate is conveyed in its longitudinal direction,and is stretched in a direction (TD) perpendicular to its conveyingdirection (MD).

The stretching temperature of the laminate may be set to any appropriatevalue depending on, for example, a formation material for the resinsubstrate and the stretching mode. When the in-air stretching mode isadopted, the stretching temperature is preferably equal to or higherthan the glass transition temperature (Tg) of the resin substrate, morepreferably Tg+10° C. or more, particularly preferably Tg+15° C. or more.Meanwhile, the stretching temperature of the laminate is preferably 170°C. or less. Performing the stretching at such temperature suppressesrapid progress of the crystallization of the PVA-based resin, therebyenabling the suppression of a problem due to the crystallization (suchas the inhibition of the orientation of the PVA-based resin membrane bythe stretching).

When the underwater stretching mode is adopted as a stretching mode, theliquid temperature of a stretching bath is preferably from 40° C. to 85°C., more preferably from 50° C. to 85° C. At such temperature, thePVA-based resin membrane can be stretched at a high ratio while itsdissolution is suppressed. Specifically, as described above, the glasstransition temperature (Tg) of the resin substrate is preferably 60° C.or more in relation to the formation of the PVA-based resin membrane. Inthis case, when the stretching temperature falls short of 40° C., thereis a risk that the stretching cannot be satisfactorily performed even inconsideration of the plasticization of the resin substrate by water. Onthe other hand, as the temperature of the stretching bath increases, thesolubility of the PVA-based resin membrane is raised and hence excellentoptical characteristics may not be obtained.

When the underwater stretching mode is adopted, the laminate ispreferably stretched while being immersed in an aqueous solution ofboric acid (in-boric-acid-solution stretching). The use of the aqueoussolution of boric acid as the stretching bath can impart, to thePVA-based resin membrane, rigidity enough to withstand a tension to beapplied at the time of the stretching and such water resistance that themembrane does not dissolve in water. Specifically, boric acid canproduce a tetrahydroxyborate anion in the aqueous solution to cross-linkwith the PVA-based resin through a hydrogen bond. As a result, thePVA-based resin membrane can be satisfactorily stretched with the aid ofthe rigidity and the water resistance imparted thereto, and hence apolarizing film having excellent optical characteristics can beproduced.

The aqueous solution of boric acid is preferably obtained by dissolvingboric acid and/or a borate in water as a solvent. The concentration ofboric acid is preferably from 1 part by weight to 10 parts by weightwith respect to 100 parts by weight of water. Setting the concentrationof boric acid to 1 part by weight or more can effectively suppress thedissolution of the PVA-based resin membrane, thereby enabling theproduction of a polarizing film having additionally highcharacteristics. It should be noted that an aqueous solution obtained bydissolving a boron compound such as borax, glyoxal, glutaric aldehyde,or the like as well as boric acid or the borate in the solvent may alsobe used.

The stretching bath (aqueous solution of boric acid) is preferablycompounded with an iodide. Compounding the bath with the iodide cansuppress the elution of iodine that the PVA-based resin membrane hasbeen caused to adsorb. Specific examples of the iodide are as describedabove. The concentration of the iodide is preferably from 0.05 part byweight to 15 parts by weight, more preferably from 0.5 part by weight to8 parts by weight with respect to 100 parts by weight of water.

The laminate is preferably immersed in the stretching bath for a time offrom 15 seconds to 5 minutes.

The stretching ratio (maximum stretching ratio) of the laminate ispreferably 5.0 times or more with respect to the original length of thelaminate. Such high stretching ratio can be achieved by adopting, forexample, the underwater stretching mode (in-boric-acid-solutionstretching). It should be noted that the term “maximum stretching ratio”as used in this specification refers to a stretching ratio immediatelybefore the rupture of the laminate. The stretching ratio at which thelaminate ruptures is separately identified and a value lower than thevalue by 0.2 is the maximum stretching ratio.

The underwater stretching treatment is preferably performed after thedyeing treatment.

(Insolubilizing Treatment)

The insolubilizing treatment is typically performed by immersing thePVA-based resin membrane in an aqueous solution of boric acid.Particularly when the underwater stretching mode is adopted, waterresistance can be imparted to the PVA-based resin membrane by subjectingthe membrane to the insolubilizing treatment. The concentration of theaqueous solution of boric acid is preferably from 1 part by weight to 4parts by weight with respect to 100 parts by weight of water. The liquidtemperature of an insolubilizing bath (the aqueous solution of boricacid) is preferably from 20° C. to 40° C. The insolubilizing treatmentis preferably performed after the production of the laminate and beforethe dyeing treatment or the underwater stretching treatment.

(Cross-Linking Treatment)

The cross-linking treatment is typically performed by immersing thePVA-based resin membrane in an aqueous solution of boric acid. Waterresistance can be imparted to the PVA-based resin membrane by subjectingthe membrane to the cross-linking treatment. The concentration of theaqueous solution of boric acid is preferably from 1 part by weight to 4parts by weight with respect to 100 parts by weight of water. Inaddition, when the cross-linking treatment is performed after the dyeingtreatment, the solution is preferably further compounded with an iodide.Compounding the solution with the iodide can suppress the elution ofiodine that the PVA-based resin membrane has been caused to adsorb. Thecompounding amount of the iodide is preferably from 1 part by weight to5 parts by weight with respect to 100 parts by weight of water. Specificexamples of the iodide are as described above. The liquid temperature ofa cross-linking bath (the aqueous solution of boric acid) is preferablyfrom 20° C. to 50° C. The cross-linking treatment is preferablyperformed before the underwater stretching treatment. In a preferredembodiment, the dyeing treatment, the cross-linking treatment, and theunderwater stretching treatment are performed in the stated order.

(Washing Treatment)

The washing treatment is typically performed by immersing the PVA-basedresin membrane in an aqueous solution of potassium iodide.

(Drying Treatment)

The drying temperature in the drying treatment is preferably from 30° C.to 100° C.

B. Protective Layer

Any appropriate resin film may be used as the protective layer. As aformation material for the resin film, there are given, for example: a(meth)acrylic resin, a cellulose-based resin such as diacetylcelluloseor triacetylcellulose; a cycloolefin-based resin such as anorbornene-based resin; an olefin-based resin such as polypropylene; anester-based resin such as a polyethylene terephthalate-based resin; apolyamide-based resin; a polycarbonate-based resin; and a copolymerresin thereof. It should be noted that the term “(meth)acrylic resin”refers to an acrylic resin and/or a methacrylic resin.

In one embodiment, a (meth)acrylic resin having a glutarimide structureis used as the (meth)acrylic resin. The (meth)acrylic resin having aglutarimide structure (hereinafter sometimes referred to as glutarimideresin) is described in, for example, Japanese Patent ApplicationLaid-open No. 2006-309033, Japanese Patent Application Laid-open No.2006-317560, Japanese Patent Application Laid-open No. 2006-328329,Japanese Patent Application Laid-open No. 2006-328334, Japanese PatentApplication Laid-open No. 2006-337491, Japanese Patent ApplicationLaid-open No. 2006-337492, Japanese Patent Application Laid-open No.2006-337493, Japanese Patent Application Laid-open No. 2006-337569,Japanese Patent Application Laid-open No. 2007-009182, Japanese PatentApplication Laid-open No. 2009-161744, and Japanese Patent ApplicationLaid-open No. 2010-284840. The descriptions thereof are incorporatedherein by reference.

The resin film is formed by any appropriate method. Examples of thefilm-forming method include a melt extrusion method, a solution castingmethod, a calender method, and a compression forming method. Of those, amelt extrusion method is preferred. In addition, the resin film may besubjected to stretching treatment.

The thickness of the protective layer is generally from 10 μm to 100 μm,preferably from 10 μm to 50 μm, more preferably from 10 μm to 30 μm.

C. Adhesion Layer

The adhesion layer may be formed of any appropriate adhesive and/orpressure-sensitive adhesive. The adhesion layer has a thickness of 0.7μm or more, preferably 0.8 μm or more, more preferably 0.9 μm or more.When such adhesion layer is formed, the generation of air bubbles can beeffectively suppressed, and thus a polarizing plate excellent inexternal appearance can be obtained. As described above, a polarizingfilm having a small thickness has a high iodine concentration, and thepolarizing film tends to be hard when having a high iodineconcentration. In the lamination of the protective layer on thepolarizing film through the intermediation of the adhesion layer, whenthe polarizing film is hard, air bubbles are liable to be generatedbetween the polarizing film and the adhesion layer. The provision of theadhesion layer having such thickness on the polarizing film having asmall thickness (a thickness of 10 μm or less) is one feature of thepresent invention. On the other hand, the thickness of the adhesionlayer is preferably 2 μm or less, more preferably 1.7 μm or less,particularly preferably 1.5 μm or less. When the thickness falls withinsuch range, durability can be kept. Specifically, the degradation ofoptical characteristics under high humidity can be suppressed.

The adhesion layer has a percentage of bulk water absorption of 10 wt %or less, preferably 8 wt % or less, more preferably 5 wt % or less,particularly preferably 2 wt % or less. When the percentage of bulkwater absorption is set to 10 wt % or less, a polarizing plate that alsohas excellent durability can be obtained. Specifically, when thepolarizing plate is placed under a high-temperature and high-humidityenvironment, the penetration of water into the polarizing film issuppressed, and thus problems such as the generation of speckles and thedegradation of optical characteristics can be suppressed. On the otherhand, the percentage of bulk water absorption of the adhesion layer ispreferably 0.05 wt % or more. When the percentage of bulk waterabsorption is set to 0.05 wt % or more, the adhesion layer canappropriately absorb moisture contained in the polarizing film whenbrought into contact with the polarizing film, and thus an externalappearance failure (such as cissing or air bubbles) in the polarizingplate to be obtained can be suppressed. It should be noted that thepercentage of bulk water absorption is measured in conformity with thetesting method for a percentage of water absorption described in JIS K7209. Specifically, the percentage of bulk water absorption is apercentage of water absorption in the case where an adhesion layer aftercuring is immersed in pure water at 23° C. for 24 hours, and isdetermined by the following equation: percentage of bulk waterabsorption (%)=[{(weight of adhesion layer after immersion)−(weight ofadhesion layer before immersion)}/(weight of adhesion layer beforeimmersion)]×100.

The adhesion layer has a glass transition temperature Tg of preferably60° C. or more, more preferably 70° C. or more, still more preferably75° C. or more, particularly preferably 100° C. or more, most preferably120° C. or more. On the other hand, the glass transition temperature Tgof the adhesion layer is preferably 300° C. or less, more preferably240° C. or less, particularly preferably 180° C. or less. When the glasstransition temperature Tg falls within such range, a polarizing plateexcellent in flexibility and excellent in durability can be obtained.The glass transition temperature is determined from the peak toptemperature of tan δ obtained through dynamic viscoelasticitymeasurement. For example, the glass transition temperature may bemeasured using a dynamic viscoelasticity measuring apparatus availableunder the trade name “RSAIII” from TA Instruments under the followingmeasurement conditions.

Sample size: 10 mm in width and 30 mm in length,Clamp distance: 20 mm,Measurement mode: tensile, Frequency: 1 Hz, Rate of temperatureincrease: 5° C./min

The adhesion layer has a storage modulus in the region of 70° C. or lessof preferably from 1.0×10⁶ Pa to 1.0×10¹⁰ Pa, more preferably from1.0×10⁷ Pa to 1.0×10¹⁰ Pa. When the storage modulus falls within suchrange, the generation of the air bubbles can be more effectivelysuppressed. In addition, a crack in the polarizing plate occurring uponapplication of a heat cycle (for example, from −40° C. to 80° C.) can besuppressed. The storage modulus may be measured by the dynamicviscoelasticity measurement.

The adhesion layer satisfying the above-mentioned percentage of bulkwater absorption is formed by, for example, curing a curable adhesive.Examples of the curable adhesive include a radicalpolymerization-curable adhesive and a cationic polymerization-curableadhesive. The curable adhesive contains a curable compound as a maincomponent. The percentage of bulk water absorption may be adjusted byappropriately selecting, for example, the kind and content of thecurable compound.

(Radical Polymerization-Curable Adhesive)

The radical polymerization-curable adhesive contains a radicallypolymerizable compound as the curable compound. The radicallypolymerizable compound may be a compound capable of being cured with anactive energy ray, or may be a compound capable of being cured withheat. Examples of the active energy ray include an electron beam, UVlight, and visible light.

As the radically polymerizable compound, for example, there may be useda compound having a radically polymerizable functional group having acarbon-carbon double bond, such as a (meth)acryloyl group or a vinylgroup. A polyfunctional radically polymerizable compound is preferablyused as the radically polymerizable compound. The radicallypolymerizable compounds may be used alone or in combination. Inaddition, the polyfunctional radically polymerizable compound and amonofunctional radically polymerizable compound may be used incombination.

A compound having a high log P value (octanol/water partitioncoefficient) (preferably 2 or more, more preferably 3 or more, stillmore preferably 4 or more) is preferably used as the curable compound.In addition, a compound having a high log P value is preferably selectedas the radically polymerizable compound as well. The log P value of theradically polymerizable compound is preferably 2 or more, morepreferably 3 or more, still more preferably 4 or more. When the log Pvalue falls within such range, the polarizing film can be prevented frombeing deteriorated by moisture, and thus a polarizing plate excellent indurability can be obtained. The log P value may be measured inconformity with the shake flask method described in JIS Z 7260. Inaddition, the log P value may also be determined through calculationusing, for example, ChemDraw Ultra manufactured by CambridgeSoft.

Examples of the polyfunctional radically polymerizable compound include:esterified products of a (meth)acrylate and a polyhydric alcohol, suchas tripropylene glycol di(meth)acrylate, tetraethylene glycoldi(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanedioldi(meth)acrylate, 1,10-decanediol diacrylate, 2-ethyl-2-butylpropanedioldi(meth)acrylate, bisphenol A di(meth)acrylate, bisphenol A-ethyleneoxide adduct di(meth)acrylate, bisphenol A-propylene oxide adductdi(meth)acrylate, bisphenol A diglycidyl ether di(meth)acrylate,neopentyl glycol di(meth)acrylate, tricyclodecanedimethanoldi(meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate,dioxane glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate,pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol penta(meth)acrylate, dipentaerythritolhexa(meth)acrylate, and EO-modified diglycerin tetra(meth)acrylate;9,9-bis[4-(2-(meth)acryloyloxyethoxy)phenyl]fluorene; epoxy(meth)acrylate; urethane (meth)acrylate; and polyester (meth)acrylate.

A compound having a high log P value is preferably used as thepolyfunctional radically polymerizable compound. Examples of suchcompound include: an alicyclic (meth)acrylate such astricyclodecanedimethanol di(meth)acrylate (log P=3.05) or isobornyl(meth)acrylate (log P=3.27); a long-chain aliphatic (meth)acrylate suchas 1,9-nonanediol di(meth)acrylate (log P=3.68) or 1,10-decanedioldiacrylate (log P=4.10); a multibranched (meth)acrylate such asneopentyl glycol hydroxypivalate-(meth)acrylic acid adduct (log P=3.35)or 2-ethyl-2-butylpropanediol di(meth)acrylate (log P=3.92); and anaromatic ring-containing (meth)acrylate such as bisphenol Adi(meth)acrylate (log P=5.46), bisphenol A-ethylene oxide (4 mole)adduct di(meth)acrylate (log P=5.15), bisphenol A-propylene oxide (2mole) adduct di(meth)acrylate (log P=6.10), bisphenol A-propylene oxide(4 mole) adduct di(meth)acrylate (log P=6.43),9,9-bis[4-(2-(meth)acryloyloxyethoxy)phenyl]fluorene (log P=7.48), orp-phenylphenol (meth)acrylate (log P=3.98).

An example of the monofunctional radically polymerizable compound is a(meth)acrylamide derivative having a (meth)acrylamide group. When the(meth)acrylamide derivative is used, an adhesion layer excellent inadhesion property can be formed with high productivity. Specificexamples of the (meth)acrylamide derivative include: an N-alkylgroup-containing (meth)acrylamide derivative such asN-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide,N,N-diethyl(meth)acrylamide, N-isopropyl(meth)acrylamide,N-butyl(meth)acrylamide, or N-hexyl(meth)acrylamide; an N-hydroxyalkylgroup-containing (meth)acrylamide derivative such asN-methylol(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, orN-methylol-N-propane(meth)acrylamide; an N-aminoalkyl group-containing(meth)acrylamide derivative such as aminomethyl(meth)acrylamide oraminoethyl(meth)acrylamide; an N-alkoxy group-containing(meth)acrylamide derivative such as N-methoxymethylacrylamide orN-ethoxymethylacrylamide; and an N-mercaptoalkyl group-containing(meth)acrylamide derivative such as mercaptomethyl(meth)acrylamide ormercaptoethyl(meth)acrylamide. In addition, as a heterocycle-containing(meth)acrylamide derivative in which the nitrogen atom of its(meth)acrylamide group forms a heterocycle, for example, there may beused N-acryloylmorpholine, N-acryloylpiperidine,N-methacryloylpiperidine, or N-acryloylpyrrolidine. Of those, anN-hydroxyalkyl group-containing (meth)acrylamide derivative ispreferred, and N-hydroxyethyl(meth)acrylamide is more preferred.

In addition, as the monofunctional radically polymerizable compound, forexample, there may be used a (meth)acrylic acid derivative having a(meth)acryloyloxy group; a carboxy group-containing monomer such as(meth)acrylic acid, carboxyethyl acrylate, carboxypentyl acrylate,itaconic acid, maleic acid, fumaric acid, crotonic acid, or isocrotonicacid; a lactam-based vinyl monomer such as N-vinylpyrrolidone,N-vinyl-ε-caprolactam, or methylvinylpyrrolidone; and a vinyl-basedmonomer having a nitrogen-containing heterocycle such as vinylpyridine,vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine,vinylpyrrole, vinylimidazole, vinyloxazole, or vinylmorpholine.

When the polyfunctional radically polymerizable compound and themonofunctional radically polymerizable compound are used in combination,the content of the polyfunctional radically polymerizable compound ispreferably from 20 wt % to 97 wt %, more preferably from 50 wt % to 95wt %, still more preferably from 75 wt % to 92 wt %, particularlypreferably from 80 wt % to 92 wt % with respect to the total amount ofthe radically polymerizable compounds. The content of the monofunctionalradically polymerizable compound is preferably from 3 wt % to 80 wt %,more preferably from 5 wt % to 50 wt %, still more preferably from 8 wt% to 25 wt %, particularly preferably from 8 wt % to 20 wt % withrespect to the total amount of the radically polymerizable compounds.When the contents fall within such ranges, a polarizing plate excellentin durability can be obtained.

The radical polymerization-curable adhesive may further contain anyother additive. When the radical polymerization-curable adhesivecontains a curable compound capable of being cured with an active energyray, the adhesive may further contain, for example, aphotopolymerization initiator, a photoacid generator, or a silanecoupling agent. In addition, when the radical polymerization-curableadhesive contains a curable compound capable of being cured with heat,the adhesive may further contain, for example, a thermal polymerizationinitiator or a silane coupling agent. In addition, examples of the otheradditive include a polymerization inhibitor, a polymerization initiationaid, a leveling agent, a wettability improver, a surfactant, aplasticizer, a UV absorber, an inorganic filler, a pigment, and a dye.

(Cationic Polymerization-Curable Adhesive)

The cationic polymerization-curable adhesive contains a cationicallypolymerizable compound as the curable compound. An example of thecationically polymerizable compound is a compound having an epoxy groupand/or an oxetanyl group. A compound having at least two epoxy groups inthe molecule is preferably used as the compound having an epoxy group.Examples of the compound having an epoxy group include: a compoundhaving at least two epoxy groups and at least one aromatic ring(aromatic epoxy compound); and a compound having at least two epoxygroups in the molecule, at least one of which is formed between twoadjacent constituent carbon atoms of an alicyclic ring (alicyclic epoxycompound).

The cationic polymerization-curable adhesive preferably contains aphotocationic polymerization initiator. The photocationic polymerizationinitiator generates a cationic species or a Lewis acid throughirradiation with an active energy ray such as visible light, UV light,an X-ray, or an electron beam, to thereby initiate a polymerizationreaction of an epoxy group or an oxetanyl group. In addition, thecationic polymerization-curable adhesive may further contain theadditive.

The adhesion layer is formed by, for example, applying the curableadhesive onto the polarizing film or the protective layer, subsequentlybonding the protective layer or the polarizing film thereonto, and thencuring the curable adhesive. It should be noted that the protectivelayer may have an easy-adhesion layer formed thereon, or may besubjected to surface modification treatment, in advance. Examples of thesurface modification treatment include corona treatment, plasmatreatment, and saponification treatment.

Any appropriate method may be adopted as a method of applying thecurable adhesive, depending on the viscosity of the adhesive and adesired thickness of the adhesion layer. An example of the applicationmethod is application with a reverse coater, a gravure coater (direct,reverse, or offset), a bar reverse coater, a roll coater, a die coater,a bar coater, a rod coater, or the like. In addition, application usinga dipping method may be adopted.

Any appropriate method may be adopted as a method of curing the curableadhesive. When the curable adhesive contains a curable compound capableof being cured with an active energy ray, the adhesive may be cured byradiating the active energy ray from the polarizing film side or theprotective layer side. From the viewpoint of preventing thedeterioration of the polarizing film, it is preferred to radiate theactive energy ray from the protective layer side. Conditions such as thewavelength and dose of the active energy ray may be set to anyappropriate conditions depending on, for example, the kind of thecurable compound to be used. When the curable adhesive contains acurable compound capable of being cured with heat, the adhesive may becured through heating. Conditions for the heating may be set to anyappropriate conditions depending on, for example, the kind of thecurable compound to be used.

EXAMPLES

The present invention is specifically described by way of Examples.However, the present invention is not limited to Examples. It should benoted that measurement methods for respective characteristics are asdescribed below, and a protective layer, adhesives, and active energyray used in Examples and Comparative Examples are as described below.

(Measurement Methods)

1. Thickness

A thickness was measured using a digital micrometer (manufactured byANRITSU CORPORATION, trade name: “KC-351C”).

2. Water Vapor Transmission Rate

Measurement was performed on the basis of the testing methods fordetermination of the water vapor transmission rate of moisture-proofpackaging materials (dish method) described in JIS Z 0208.

3. Percentage of Bulk Water Absorption

A curable adhesive was cured under the same conditions as those ofExample 1 to be described later to produce a cured product forevaluation having a thickness of 100 μm (weight: M1 g). The curedproduct for evaluation was immersed in pure water at 23° C. for 24 hoursand was then taken out, and water on its surface was wiped off. Afterthat, the weight (M2 g) of the cured product for evaluation after theimmersion was measured. A percentage of bulk water absorption wascalculated from the weight M1 g of the cured product for evaluationbefore the immersion and the weight M2 g of the cured product forevaluation after the immersion in accordance with the expression{(M2−M1)/M1}×100(%).

(Protective Layer)

Pellets of a methacrylic resin having a glutarimide ring unit were driedat 100.5 kPa and 100° C. for 12 hours, and were formed into a film shapeby being extruded from a T-die at a die temperature of 270° C. throughthe use of a single-screw extruder. The film was stretched in itsconveying direction (MD direction) under an atmosphere having atemperature higher than the Tg of the resin by 10° C., and was thenstretched in a direction (TD direction) perpendicular to the conveyingdirection of the film under an atmosphere having a temperature higherthan the Tg of the resin by 7° C. Thus, an acrylic film having athickness of 40 μm and a water vapor transmission rate of 80 g/m² wasobtained.

(Curable Adhesive)

Respective components were mixed as shown in Table 1 and stirred at 50°C. for 1 hour to obtain a curable adhesive A and a curable adhesive Beach capable of being cured with an active energy ray. It should benoted that the curable adhesive A had a percentage of bulk waterabsorption of 1.3 wt %, and the curable adhesive B had a percentage ofbulk water absorption of 68.2 wt %.

TABLE 1 Curable adhesive A Curable adhesive B Radically MonofunctionalHEAA 10 parts by weight 35 parts by weight polymerizable ACMO — 40 partsby weight compound FA-THFM 10 parts by weight  0 parts by weightPolyfunctional LIGHT ACRYLATE 80 parts by weight  0 parts by weightDCP-A TPGDA — 25 parts by weight Radical polymerization initiatorIRGACURE 907  3 parts by weight  3 parts by weight KAYACUREDETX-S  3parts by weight  3 parts by weight

The radically polymerizable compounds in Table 1 are as follows:

HEAA: hydroxyethylacrylamide, log P=−0.56, Tg of its homopolymer=123°C., manufactured by KOHJIN Holdings Co., Ltd;

ACMO: acryloylmorpholine, log P=−0.20, Tg of its homopolymer=150° C.,manufactured by KOHJIN Holdings Co., Ltd;

FA-THFM: tetrahydrofurfuryl (meth)acrylate, log P=1.13, Tg of itshomopolymer=45° C., manufactured by Hitachi Chemical Co., Ltd;

LIGHT ACRYLATE DCP-A: tricyclodecanedimethanol diacrylate, log P=3.05,Tg of its homopolymer=134° C., manufactured by KYOEISHA CHEMICAL Co.,LTD; and

TPGDA: tripropylene glycol diacrylate, log P=1.68, Tg of itshomopolymer=69° C., manufactured by TOAGOSEI CO., LTD. (ARONIX M-220).

The radical polymerization initiators are as follows:

IRGACURE 907 (2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one),log P=2.09, manufactured by BASF; and

KAYACURE DETX-S (diethylthioxanthone), log P=5.12, manufactured byNippon Kayaku Co., Ltd.

(Active Energy Ray)

The active energy ray used was visible light (gallium-doped metal halidelamp, irradiation apparatus: “Light Hammer 10” manufactured by Fusion UVSystems, Inc., valve: V valve, peak illuminance: 1,600 mW/cm²,cumulative dose: 1,000 mJ/cm² (wavelength: 380 to 440 nm)). It should benoted that the illuminance of the visible light was measured usingSola-Check System manufactured by Solatell Ltd.

Example 1 Polarizing Film

As a resin substrate, there was prepared an amorphous polyethyleneterephthalate (IPA-copolymerized PET) film having a thickness of 100 μm,a Tg of 75° C., and 7 mol % of an isophthalic acid unit. A surface ofthe film was subjected to corona treatment (58 W/m²/min).

PVA (average polymerization degree: 4,200, saponification degree: 99.2mol %) having added thereto 1 wt % of acetoacetyl-modified PVA(manufactured by The Nippon Synthetic Chemical Industry Co., Ltd., tradename: GOHSEFIMER 2200, average polymerization degree: 1,200,saponification degree: 98.5 mol % or more, acetoacetylation degree: 5%)was prepared, and an aqueous solution containing 5.5 wt % of thePVA-based resin was prepared. The aqueous solution was applied onto thecorona-treated surface of the resin substrate so as to have a filmthickness after drying of 9 μm, and was dried with hot air under anatmosphere of 60° C. for 10 minutes to form a PVA-based resin layerhaving a thickness of 9 μm on the resin substrate. Thus, a laminate wasproduced.

The resultant laminate was first stretched in air at 130° C. at a ratioof 1.8 times (preliminary in-air stretching).

Next, the laminate was immersed in an aqueous solution of boric acidhaving a liquid temperature of 30° C. for 30 seconds to insolubilize thePVA-based resin layer. The aqueous solution of boric acid in this stepwas adjusted so as to have a boric acid content of 3 parts by weightwith respect to 100 parts by weight of water.

Then, the laminate was dyed by being immersed in a dyeing liquid havinga liquid temperature of 30° C. and containing iodine and potassiumiodide for any appropriate period of time so that a polarizing film tobe obtained had a single axis transmittance of from 40 to 44%. Thedyeing liquid contained water as a solvent, and was adjusted so as tohave an iodine concentration within the range of from 0.1 to 0.4 wt %, apotassium iodide concentration within the range of from 0.7 to 2.8 wt %,and a concentration ratio between iodine and potassium iodide of 1:7.

Next, the laminate was immersed in an aqueous solution of boric acid at30° C. for 60 seconds to subject the PVA resin layer having adsorbedthereon iodine to cross-linking treatment. The aqueous solution of boricacid in this step was adjusted so as to have a boric acid content of 3parts by weight with respect to 100 parts by weight of water, and apotassium iodide content of 3 parts by weight with respect to 100 partsby weight of water.

Further, the laminate was stretched in an aqueous solution of boric acidat a stretching temperature of 70° C. in the same direction as that inthe previous preliminary in-air stretching at a ratio of 3.05 times(final stretching ratio: 5.50 times). The aqueous solution of boric acidin this step was adjusted so as to have a boric acid content of 4 partsby weight with respect to 100 parts by weight of water, and a potassiumiodide content of 5 parts by weight with respect to 100 parts by weightof water.

Next, the laminate was washed with an aqueous solution adjusted so as tohave a potassium iodide content of 4 parts by weight with respect to 100parts by weight of water, and was dried with hot air at 60° C. to obtaina polarizing film having a thickness of 3.7 μm on the resin substrate.

(Polarizing Plate)

The acrylic film having a thickness of 40 μm was bonded onto theobtained polarizing film (onto the surface on the side opposite to theresin substrate) through the intermediation of the curable adhesive A.Specifically, the curable adhesive was applied onto the acrylic filmusing an MCD coater (manufactured by FUJI KIKAI KOGYO Co., Ltd., cellshape: honeycomb, number of gravure roll lines: 1,000 lines/inch,rotational speed: 140%/relative to line speed) so as to have a thicknessof 1.0 μm, and the whole was bonded using a rolling mill. The bondingwas performed at a line speed of 25 m/min.

After that, the resultant was heated from the acrylic film side to 50°C. using an IR heater, and was irradiated with the visible light fromthe acrylic film side to cure the curable adhesive. Then, the resultantwas dried with hot air at 70° C. for 3 minutes, and the PET film waspeeled from the polarizing film to obtain a polarizing plate.

Example 2

A polarizing plate was produced in the same manner as in Example 1except that in the production of the polarizing film, a PVA-based resinlayer having a thickness of 11 μm was formed on the resin substrate toform a polarizing film having a thickness of 4.7 μm.

Example 3

A polarizing plate was produced in the same manner as in Example 1except that in the production of the polarizing film, a PVA-based resinlayer having a thickness of 17 μm was formed on the resin substrate toform a polarizing film having a thickness of 6.9 μm.

Example 4

A polarizing plate was produced in the same manner as in Example 1except that in the production of the polarizing film, a PVA-based resinlayer having a thickness of 22 μm was formed on the resin substrate toform a polarizing film having a thickness of 9.1 μm.

Example 5

A polarizing plate was produced in the same manner as in Example 2except that in the production of the polarizing plate, the thickness ofthe adhesion layer was changed to 0.8 μm.

Example 6

A polarizing plate was produced in the same manner as in Example 2except that in the production of the polarizing plate, the thickness ofthe adhesion layer was changed to 1.5 μm.

Comparative Example 1

A polarizing plate was produced in the same manner as in Example 2except that in the production of the polarizing plate, the thickness ofthe adhesion layer was changed to 0.5 μm.

Comparative Example 2

A polarizing plate was produced in the same manner as in Example 2except that in the production of the polarizing plate, the curableadhesive B was used in place of the curable adhesive A.

The polarizing film obtained in each of Examples and ComparativeExamples was subjected to the following measurement.

(Optical Characteristics of Polarizing Film)

The single axis transmittance (Ts), parallel transmittance (Tp), andcrossed transmittance (Tc) of the polarizing film were measured using anultraviolet and visible spectrophotometer (V7100 manufactured by JASCOCorporation), and its polarization degree (P) was determined by thefollowing equation. The transmittances are Y values measured with thetwo-degree field of view (C light source) of JIS Z 8701 and subjected tovisibility correction. The measurement was performed under a state inwhich the protective layer (acrylic film) was bonded onto the polarizingfilm (state of a polarizing plate) so as to facilitate the handling ofthe polarizing film. The absorption of light by the protective layer isnegligibly low as compared to the absorption of light by the polarizingfilm, and hence the transmittance of the polarizing plate was adopted asthe transmittance of the polarizing film.

Polarization degree(P)={(Tp−Tc)/(Tp+Tc)}^(1/2)×100

(Calculation of Absorbance)

The parallel transmittance Tp and crossed transmittance Tc measured inthe transmittance and polarization degree measurement described abovewere used in the following equation to calculate a transmittance ka inthe case where polarized light parallel to the absorption axis of thepolarizing film was allowed to enter, and then the absorbance of thepolarizing film in the absorption axis direction thereof (absorbance inthe case where polarized light parallel to the absorption axis of thepolarizing film is allowed to enter) Aa was calculated from ka. In thecalculation, values at measurement wavelengths of from 380 to 780 nmwere used as they were as Tp and Tc instead of the Y values subjected tovisibility correction.

ka=(1/2)^(1/2)(Tp+Tc)^(1/2)/(Tp−Tc)^(1/2)

Aa=−log₁₀(ka)

(Raman Spectrometry)

As illustrated in FIG. 6, the central part of the obtained polarizingplate was cut in the absorption axis direction (stretching direction) ofthe polarizing film and in the thickness direction of the polarizingfilm using an ultramicrotome (manufactured by LEICA MICROSYSTEMS,product name: “LEICA ULTRACUT UCT” or “LEICA EM UC7”), to produce anultrathin section sample measuring about 100 nm in a directionperpendicular to the absorption axis direction of the polarizing filmand to the thickness direction of the polarizing film.

The apparatus and conditions used in Raman spectrometry are as describedbelow.

Apparatus: Laser Raman microscope, manufactured by Jobin Yvon S.A.S,LabRAM HR800 (manufactured by HORIBA Jobin Yvon SAS, HR800)

Excitation wavelength: 514.5 nm

Grating: 1,800 gr/mm

Objective lens: 100× (numerical aperture: 0.9)

Measurement pitch: 0.1 μm

As illustrated in FIG. 7, the polarizing film cross-section of theultrathin section sample was subjected to the measurement of Ramanspectra at measurement points at intervals of 0.1 μm in the thicknessdirection of the polarizing film.

Laser light was allowed to enter so that its polarization plane wasparallel to the absorption axis direction (stretching direction) of thepolarizing film and perpendicular to the polarizing film cross-sectionof the ultrathin section sample. In addition, an analyzer was placedbehind the ultrathin section sample. The polarization plane of theanalyzer was set parallel to the polarization plane of the laser light.

On the basis of the above-mentioned measurement conditions, theresolution, that is, the spot diameter (half-value width) of the laserlight on the sample was 0.7 μm. When the center of the spotcross-section of the laser light was located at a position of 0.5 μmfrom the polarizing film surface, the spot cross-section of the laserlight substantially corresponded to the center of a portion ranging fromthe polarizing film surface to a depth of 1 μm in the thicknessdirection of the polarizing film, and an error due to Raman scatteringfrom I₃ ⁻ that was present in a portion other than the portion rangingfrom the polarizing film surface to a depth of 1 μm in the thicknessdirection of the polarizing film or from air was small, which enabledsatisfactory approximation of Is.

In each of the Raman spectra of Examples and Comparative Examples, asshown in FIG. 3, a peak corresponding to I₃ ⁻ was observed around 108cm⁻¹, and a peak corresponding to I₅ ⁻ was observed around 158 cm⁻¹.

(Calculation of Integrated Intensity Distribution of I₃ ⁻)

The Raman spectrum obtained at each measurement point was subjected tobaseline correction to determine an integrated intensity in a wavenumberinterval from 90 cm⁻¹ to 120 cm⁻¹.

The baseline correction was performed as follows: in the wavenumberinterval from 90 cm⁻¹ to 120 cm⁻¹, a straight line connecting therespective points of a Raman intensity at a wavenumber of 90 cm⁻¹ and aRaman intensity at a wavenumber of 120 cm⁻¹ was used to approximate thebaseline of the Raman spectrum as a straight line, and a distance fromthe approximation straight line was defined as a Raman intensity tocorrect the slope of the baseline at the time of the measurement (seeFIG. 3). An integrated intensity distribution in the thickness directionof the polarizing film was determined from the resultant integratedintensities at the respective measurement points (FIG. 4). It should benoted that the origin of the thickness direction in the figurecorresponds to the position of an inflection point to be describedlater, and it is assumed that light is allowed to enter from a negativecoordinate side.

(Calculation of Value for Aa×(is/Ia))

In FIG. 4, i.e., the graph of the integrated intensity distribution inthe thickness direction of the polarizing film, a value Ia obtained byintegrating the integrated intensity distribution in the entire intervalin the thickness direction of the polarizing film was calculated.Specifically, an integrated intensity at a position x in the thicknessdirection before smoothing processing was represented by I(x), anintegrated intensity I_(WMA)(x) after smoothing processing wasdetermined by the following equation, and I_(WMA)(x) was integrated overthe entire interval to calculate the value Ia.

I_(WMA)(x)=[I(x−0.5)×1+I(x−0.4)×2+I(x−0.3)×4+I(x−0.2)×6+I(x−0.1)×8+I(x)×10+I(x+0.1)×8+I(x+0.2)×6+I(x+0.3)×4+I(x+0.4)×2+I(x+0.5)×1]/(1+2+4+6+8+10+8+6+4+2+1)

FIG. 4 shows an example of the resultant integrated intensitydistribution after the smoothing processing.

Next, a value Is obtained by integrating the integrated intensitydistribution of an integrated intensity in the thickness direction ofthe polarizing film in the entire interval in the thickness direction ofthe polarizing film, the integrated intensity being obtained byintegrating the Raman scattering of I₃ ⁻ that was present in the portionranging from the polarizing film surface to a depth of 1 μm in thethickness direction of the polarizing film, and that was aligned in theabsorption axis direction of the polarizing film in the wavenumberinterval from 90 cm⁻¹ to 120 cm⁻¹, was approximately determined.

Specifically, first, in the integrated intensity distribution after thesmoothing processing obtained as described above in the calculation ofIa, the position of an inflection point at a rise on the side on whichlight entered was identified by determining a local maximum value in thedifferential of the integrated intensity distribution.

Next, a value I_(WMA)(0.5) for an integrated intensity after thesmoothing processing at a position of +0.5 μm from the identifiedposition of the inflection point was determined, and the value wasadopted as Is.

On the basis of the thus-obtained values for Aa, Ia, and I_(WMA)(0.5), avalue for Aa×(I(0.5)/Ia) was determined as a value for Aa×(Is/Ia) asdescribed above.

(Evaluation)

The following evaluation was performed for each of Examples andComparative Examples.

1. External Appearance Quality (Presence or Absence of Generation of AirBubbles)

The polarizing plate of each of Examples and Comparative Examples wasvisually observed for its external appearance quality.

2. Durability (Presence or Absence of Generation of Speckles)

The polarizing plate of each of Examples and Comparative Examples wasput into a heating and humidifying tester, and was then observed for thepresence or absence of the generation of speckles, to thereby evaluateits durability. Details are as described below.

The polarizing film surface of the polarizing plate that had been cutinto a size of 5 inches was bonded onto a glass plate through theintermediation of an acrylic pressure-sensitive adhesive (thickness: 20μm) to produce an evaluation sample. The evaluation sample was stored ina heating and humidifying oven at a temperature of 65° C. and a humidityof 90% for 500 h, and was then taken out from the oven and storedovernight, followed by the observation of the presence or absence of thegeneration of speckles. The observation was performed by arranging theevaluation sample and a commercially available polarizing plate(manufactured by Nitto Denko Corporation, SEG-type polarizing plate) ona backlight having a brightness of 10,000 cd/cm² so that theirabsorption axes were perpendicular to each other.

TABLE 2 Adhesive Polarizing film Percentage of External Polarizationbulk water appearance Durability Transmittance degree Thickness Aa×absorption Thickness Generation of Generation of (%) (%) (μm) (Is/Ia)(wt %) (μm) air bubbles speckles Example 1 42.3 99.975 3.7 0.81 1.3 1.0Few Absent Example 2 42.1 99.990 4.7 0.70 1.3 1.0 Few Absent Example 342.2 99.991 6.9 0.58 1.3 1.0 Few Absent Example 4 40.1 99.988 9.1 1.091.3 1.0 Few Absent Example 5 42.1 99.990 4.7 0.70 1.3 0.8 Few AbsentExample 6 42.1 99.990 4.7 0.70 1.3 1.5 Few Absent Comparative 42.199.990 4.7 0.70 1.3 0.5 Many Absent Example 1 Comparative 42.1 99.9904.7 0.70 68.2 1.0 Few Present Example 2

In each of Examples, no problem was found in both external appearancequality and durability. In Comparative Example 1, there was a problem inexternal appearance quality due to the generation of a large number ofair bubbles. In Comparative Example 2, the durability was poor andstreak-like speckles were generated after the heating and humidifyingtest as shown in FIG. 8A.

The polarizing plate of the present invention is suitably used for animage display apparatus. Specifically, the polarizing plate of thepresent invention is suitably used for liquid crystal panels of, forexample, liquid crystal televisions, liquid crystal displays, mobilephones, digital cameras, video cameras, portable game machines, carnavigation systems, copying machines, printers, facsimile machines,timepieces, and microwave ovens, and anti-reflection plates of organicEL devices.

What is claimed is:
 1. A polarizing plate, comprising: a polarizing filmhaving a thickness of 10 μm or less; and a protective layer provided onat least one side of the polarizing film through intermediation of anadhesion layer, wherein the adhesion layer has a thickness of 0.7 μm ormore, and wherein the adhesion layer has a percentage of bulk waterabsorption of 10 wt % or less.
 2. The polarizing plate according toclaim 1, wherein the polarizing film has a value for Aa×(Is/Ia) of 0.53or more, where: the Aa represents an absorbance of the polarizing filmin an absorption axis direction thereof at a wavelength of 480 nm; theIa represents a value obtained by integrating an integrated intensitydistribution of an integrated intensity in a thickness direction of thepolarizing film in an entire interval in the thickness direction of thepolarizing film, the integrated intensity being obtained by integratinga Raman spectrum of the polarizing film in a wavenumber interval from 90cm⁻¹ to 120 cm⁻¹; and the Is represents a value obtained by integratingan integrated intensity distribution of an integrated intensity in thethickness direction of the polarizing film in the entire interval in thethickness direction of the polarizing film, the integrated intensitybeing obtained by integrating Raman scattering of I₃ ⁻ that is presentin a portion ranging from a polarizing film surface to a depth of 1 μmin the thickness direction of the polarizing film, and that is alignedin the absorption axis direction of the polarizing film in thewavenumber interval from 90 cm⁻¹ to 120 cm⁻¹.
 3. The polarizing plateaccording to claim 1, wherein the thickness of the adhesion layer is 2μm or less.
 4. The polarizing plate according to claim 1, wherein thepercentage of bulk water absorption of the adhesion layer is 0.05 wt %or more.
 5. The polarizing plate according to claim 1, wherein theadhesion layer is formed by curing a curable adhesive.
 6. The polarizingplate according to claim 1, wherein the adhesion layer has a storagemodulus in a region of 70° C. or less of from 1.0×10⁶ Pa to 1.0×10¹⁰ Pa.7. An image display apparatus, comprising the polarizing plate accordingto claim 1.